This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
The potential release of oil in a marine environment including ice has been of concern since the exploration and production for hydrocarbon resources in the Arctic began in the early 1970s. It is more challenging to detect oil under the ice surface, or trapped in ice layers, than to detect an oil slick on a water surface. There have been numerous efforts directed to detecting oil under ice using acoustical reflection, ultraviolet-visible (UV-Vis) reflectance, and ground penetrating radar, among others. All of these techniques have shown some capability to detect oil under ice.
However, the methods proposed to date may have a limited range of applicability and may be susceptible to giving false positive results. Many of these techniques require traversing across the ice surface, and some also require the removal of any snow cover to ensure good ice contact with a sensor. The surface access presents logistic issues, and may limits the coverage to a small area each day. One technique that provides a direct signal from oil is reflectance of ultraviolet and visible light from a surface of the ice, which provides an absorbance measurement. This technique, which may be termed transflectance, may be limited to the detection of oil at the surface or only a few millimeters below the surface of ice. Furthermore, transflectance may be limited by the presence of snow on the surface of the ice, which may scatter the incident and reflected light, obscuring the signal from oil.
A number of other techniques have been researched to detect the presence of oil under, on, or within ice. For example, U.S. Patent Application Publication No. 2011/0181279, by Srnka et al., discloses a techniques for detecting a liquid, such as a hydrocarbon, under a surface, such as ice, snow, or water. The method may be used in an arctic region to detect oil spills, leaks, or seepages. In the techniques, a nuclear magnetic resonance (NMR) tool with an antenna sends a radio-frequency (RF) excitation pulse or signal into volume of substances being detected. An NMR response signal is detected to determine the presence of the liquid of interest. The NMR response signal may include a relaxation time element and an intensity level and may include other NMR measurements, such as a free induction signal (T2*), a spin echo signal (T2), a train of spin echo signals (T2), or a thermal equilibrium signal (T1).
Further, U.S. Patent Application Publication No. 2014/0159936, by Medlin et al., discloses using coordinated airborne and ground platforms for detecting oil covered by ice. Detecting an oil mass covered by ice includes collecting data, such as synthetic-aperture radar data, using an airborne platform moved about a search area above the ice. Once an area that may have an oil mass covered by the ice is located based upon the data, confirmation data is collected using a ground platform moved over the alert area. The confirmation data may include wideband impulse radar data, acoustic sensor data, and light detection and ranging (LIDAR) data. An oil mass covered by the ice is detected based upon the confirmation data.
Further, International Patent Application No. WO2013/071185, by Pottorf et al., discloses a technique for the detection of hydrocarbons. The method includes deploying an underwater vehicle (UV) into a body of water and directing the UV to a target location. The UV collects measurement data within the body of water at the target location, which is then analyzed to determine whether hydrocarbons are present at the target location. The measurement data may include determining chemical composition, such as the concentration of hydrocarbon or non-hydrocarbon gases, pH, or oxidation state in the body of water. Further, physical measurements may be determined, such as magnetic anomalies or gravity.
A number of other research projects have focused on the use of unmanned underwater vehicles to detect oil spills under sea ice. Many of these are summarized in Wilkinson, J., T. Maksym, and H. Singh, “Capabilities for Detection of Oil Spills Under Sea Ice from Autonomous Underwater Vehicles,” Arctic Oil Spill Response Technology Joint Industry Programme (JIP), 15 Oct. 2013.
The techniques described above are directed to measurements made from a single side of the sea ice. Any number of factors may lower the ability of these techniques to detect oil, such as oil trapped deep within layers of the sea ice.